In most vacuum cleaners, air is drawn into the apparatus and then released through the walls of a filter bag or through the back end of a metal canister. Even if a filter is fairly efficient, a small fraction of dirt and dust particles escape through the filter bag walls or from the canister. Moreover, as air is blown out through the bag or from the canister, dirt and dust particles adjacent to the area of release are disturbed and lifted into the atmosphere.
In certain industrial applications it is imperative that the quantity of particles within a room atmosphere be kept to a minimum. A cleaning apparatus which increases, even temporarily, the quantity of airborne particles may be harmful in these applications. A not insignificant number of persons suffer from a hypersensitivity to dust particles or suffer from other allergies which are affected by an increase in airborne particles. For example, a person bothered by hayfever will suffer discomfort as a result of an apparatus causing settled particles to become airborne.
Vacuum cleaners which recirculate air back into the vacuum system are known. U.S. Pat. Nos. 4,393,536 to Tapp and 3,694,848 to Alcala teach vacuum cleaners which provide some recirculation of air flow through the system in order to increase cleaning efficiency by directing a jet blast at a carpet. The jet blast elevates dirt from the carpet, whereafter the stream of air is caused to reenter the system. In the Alcala device, the suction forces surround jet nozzles except where the jets of air enter a rug. Tapp teaches a jet blast which is rearward and spaced apart from the suction forces.
It is an object of the present invention to provide a vacuum cleaning device which directs air back into the vacuum system after filtration and which does so to a greater degree than what is accomplished by prior art recirculation systems. It is a further object to utilize the recirculation of air to enhance the cleaning efficiency of a vacuum device.